General hydraulic excavators are constructed so that the multi-articulated type of work front that includes a boom and an arm is coupled to an upper bodywork so as to look up and down and so that the arm has a vertically swayable bucket at its distal end. Instead of the bucket, however, a breaker, a crusher, a grapple, or the like may be mounted to construct a working machine intended for structure dismantling work, waste dismantling work, civil engineering/construction work, and/or the like. This kind of working machine typically has one work front. However, working machines with two work fronts have been proposed in recent years. With the two work fronts, it is possible to carry out various operations that have been difficult to perform with a conventional single-front working machine alone, such as dismantling an object with one work front while gripping the object with the other work front. Accordingly, double-arm working machines are advantageous over conventional single-arm working machines in terms of operational stability and efficiency (refer to, for example, Patent Document 1 for further details of the conventional single-arm working machines).    Patent Document 1: JP-A-11-181815